This invention relates to a speed change control unit which achieves the speed change transfer control of an automatic transmission for automobiles by means of electric and hydraulic controls.
In general, an automatic transmission for automobiles using electric and hydraulic controls attains a plurality of transmission ratios by electrically detecting the vehicular speed, the throttle opening etc., determining the optimum speed change step in accordance with the running conditions of the automobile, operating predetermined solenoid valves in accordance with the outputs, and selectively operating a plurality of hydraulic servo means. This system has the disadvantages that the number of the solenoid valves increases in correspondence with the number of speed change steps of the transmission, and that the hydraulic control portion means becomes large in size.